The present invention relates to an apparatus for measuring concentrations of radioactivity in cooling lines of water disposal lines, etc. of nuclear reactors or other plants and, more particularly, to an apparatus capable of automatically measuring the concentration of radioactivity in the coolant circulating in the cooling system of a nuclear reactor. Although an explanation will be made hereinafter as to the cooling system of a nuclear reactor, it is to be understood that the apparatus of the invention is applicable also to the water disposal system of the reactor.
The inspection or observation of the concentration of radioactivity in the coolant is important and indispensable for confirming the soundness of fuel elements and checking possible corrosion of fuel cladding, thereby to ensure a good conditioned running of a nuclear reactor.
Conventionally, the measurement of the radioactivity has been made, only when it is required, by at first taking out a small quantity of sample coolant from a predetermined portion of the cooling line, filtering and chemically treating the sample in a laboratory and then measuring the radioactivity by employing a .gamma.-ray spectrometer. Thus, the conventional method of measuring the radioactivity takes more than one hour from the picking up of the sample to the completion of the measuring, which is inconvenient especially for those radionuclides having short period of half-decay such as .sup.138 Xe.sub.14.2 min., .sup.87 Kr.sub.76 min. or .sup.134 I.sub.52.4 min., since, in case of such radionuclides, the radioactivity at the time of measurement has been considerably decayed and does not represent the actual concentration of the radioactivity.
In addition, in the conventional method of measurement, dilute gases such as Kr or Xe tend to be degassed or released at the time of taking out of the sample coolant, which considerably deteriorates the evaluation of the concentration of the dilute gases. At the same time, the conventional measuring method is likely to cause radioactive contamination of the working environment and the examiner himself.
Moreover, another shortcoming or disadvantage of the conventional method resides in that it cannot suitably follow-up the change in the radioactive intensity of the coolant, which change takes place in accordance with the change in the condition or output of the reactor.